528 research outputs found
Superluminal motion of a relativistic jet in the neutron star merger GW170817
The binary neutron star merger GW170817 was accompanied by radiation across
the electromagnetic spectrum and localized to the galaxy NGC 4993 at a distance
of 41+/-3 Mpc. The radio and X-ray afterglows of GW170817 exhibited delayed
onset, a gradual rise in the emission with time as t^0.8, a peak at about 150
days post-merger, followed by a relatively rapid decline. To date, various
models have been proposed to explain the afterglow emission, including a
choked-jet cocoon and a successful-jet cocoon (a.k.a. structured jet). However,
the observational data have remained inconclusive as to whether GW170817
launched a successful relativistic jet. Here we show, through Very Long
Baseline Interferometry, that the compact radio source associated with GW170817
exhibits superluminal motion between two epochs at 75 and 230 days post-merger.
This measurement breaks the degeneracy between the models and indicates that,
while the early-time radio emission was powered by a wider-angle outflow
(cocoon), the late-time emission was most likely dominated by an energetic and
narrowly-collimated jet, with an opening angle of <5 degrees, and observed from
a viewing angle of about 20 degrees. The imaging of a collimated relativistic
outflow emerging from GW170817 adds substantial weight to the growing evidence
linking binary neutron star mergers and short gamma-ray bursts.Comment: 42 pages, 4 figures (main text), 2 figures (supplementary text), 2
tables. Referee and editor comments incorporate
Decaying into the Hidden Sector
The existence of light hidden sectors is an exciting possibility that may be
tested in the near future. If DM is allowed to decay into such a hidden sector
through GUT suppressed operators, it can accommodate the recent cosmic ray
observations without over-producing antiprotons or interfering with the
attractive features of the thermal WIMP. Models of this kind are simple to
construct, generic and evade all astrophysical bounds. We provide tools for
constructing such models and present several distinct examples. The light
hidden spectrum and DM couplings can be probed in the near future, by measuring
astrophysical photon and neutrino fluxes. These indirect signatures are
complimentary to the direct production signals, such as lepton jets, predicted
by these models.Comment: 40 pages, 5 figure
âWork it outâ: evaluation of a chronic condition self-management program for urban Aboriginal and Torres Strait Islander people, with or at risk of cardiovascular disease
Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf
The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change1, 2. The increased freshwater output from Antarctica is important in determining sea level rise1, the fate of Antarctic sea ice and its effect on the Earthâs albedo4, 5, ongoing changes in global deep-ocean ventilation6, and the evolution of Southern Ocean ecosystems and carbon cycling7, 8. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models3â5, 9 as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels10, 11, 12, 13, 14. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models
Evolutionary design of soft-bodied animats with decentralized control
We show how a biologically inspired model of multicellular development combined with a simulated evolutionary process can be used to design the morphologies and controllers of soft-bodied virtual animats. An animatâs morphology is the result of a developmental process that starts from a single cell and goes through many cell divisions, during which cells interact via simple physical rules. Every cell contains the same genome, which encodes a gene regulatory network (GRN) controlling its behavior. After the developmental stage, locomotion emerges from the coordinated activity of the GRNs across the virtual robot body. Since cells act autonomously, the behavior of the animat is generated in a truly decentralized fashion. The movement of the animat is produced by the contraction and expansion of parts of the body, caused by the cells, and is simulated using a physics engine. Our system makes possible the evolution and development of animats that can run, swim, and actively navigate toward a target in a virtual environment
A Measurement of Rb using a Double Tagging Method
The fraction of Z to bbbar events in hadronic Z decays has been measured by
the OPAL experiment using the data collected at LEP between 1992 and 1995. The
Z to bbbar decays were tagged using displaced secondary vertices, and high
momentum electrons and muons. Systematic uncertainties were reduced by
measuring the b-tagging efficiency using a double tagging technique. Efficiency
correlations between opposite hemispheres of an event are small, and are well
understood through comparisons between real and simulated data samples. A value
of Rb = 0.2178 +- 0.0011 +- 0.0013 was obtained, where the first error is
statistical and the second systematic. The uncertainty on Rc, the fraction of Z
to ccbar events in hadronic Z decays, is not included in the errors. The
dependence on Rc is Delta(Rb)/Rb = -0.056*Delta(Rc)/Rc where Delta(Rc) is the
deviation of Rc from the value 0.172 predicted by the Standard Model. The
result for Rb agrees with the value of 0.2155 +- 0.0003 predicted by the
Standard Model.Comment: 42 pages, LaTeX, 14 eps figures included, submitted to European
Physical Journal
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Vegetation forcing modulates global land monsoon and water resources in a CO2-enriched climate
The global monsoon is characterised by transitions between pronounced dry and wet seasons, affecting food security for two-thirds of the worldâs population. Rising atmospheric CO2 influences the terrestrial hydrological cycle through climate-radiative and vegetation-physiological forcings. How these two forcings affect the seasonal intensity and characteristics of monsoonal precipitation and runoff is poorly understood. Here we use four Earth System Models to show that in a CO2-enriched climate, radiative forcing changes drive annual precipitation increases for most monsoon regions. Further, vegetation feedbacks substantially affect annual precipitation in North and South America and Australia monsoon regions. In the dry season, runoff increases over most monsoon regions, due to stomatal closure-driven evapotranspiration reductions and associated atmospheric circulation change. Our results imply that flood risks may amplify in the wet season. However, the lengthening of the monsoon rainfall season and reduced evapotranspiration will shorten the water resources scarcity period for most monsoon regions
Measurement of the B+ and B-0 lifetimes and search for CP(T) violation using reconstructed secondary vertices
The lifetimes of the B+ and B-0 mesons, and their ratio, have been measured in the OPAL experiment using 2.4 million hadronic Z(0) decays recorded at LEP. Z(0) --> b (b) over bar decays were tagged using displaced secondary vertices and high momentum electrons and muons. The lifetimes were then measured using well-reconstructed charged and neutral secondary vertices selected in this tagged data sample. The results aretau(B+) = 1.643 +/- 0.037 +/- 0.025 pstau(Bo) = 1.523 +/- 0.057 +/- 0.053 pstau(B+)/tau(Bo) = 1.079 +/- 0.064 +/- 0.041,where in each case the first error is statistical and the second systematic.A larger data sample of 3.1 million hadronic Z(o) decays has been used to search for CP and CPT violating effects by comparison of inclusive b and (b) over bar hadron decays, No evidence fur such effects is seen. The CP violation parameter Re(epsilon(B)) is measured to be Re(epsilon(B)) = 0.001 +/- 0.014 +/- 0.003and the fractional difference between b and (b) over bar hadron lifetimes is measured to(Delta tau/tau)(b) = tau(b hadron) - tau((b) over bar hadron)/tau(average) = -0.001 +/- 0.012 +/- 0.008
Using intervention mapping to develop a home-based parental-supervised toothbrushing intervention for young children
BACKGROUND: Dental caries in young children is a major public health problem impacting on the child and their family in terms of pain, infection and substantial financial burden on healthcare funders. In the UK, national guidance on the prevention of dental caries advises parents to supervise their child's brushing with fluoride toothpaste until age 7. However, there is a dearth of evidence-based interventions to encourage this practice in parents. The current study used intervention mapping (IM) to develop a home-based parental-supervised toothbrushing intervention to reduce dental caries in young children. METHODS: The intervention was developed using the six key stages of the IM protocol: (1) needs assessment, including a systematic review, qualitative interviews, and meetings with a multi-disciplinary intervention development group; (2) identification of outcomes and change objectives following identification of the barriers to parental-supervised toothbrushing (PSB), mapped alongside psychological determinants outlined in the Theoretical Domains Framework (TDF); (3) selection of methods and practical strategies; (4) production of a programme plan; (5) adoption and implementation and (6) Evaluation. RESULTS: The comprehensive needs assessment highlighted key barriers to PSB, such as knowledge, skills, self-efficacy, routine setting and behaviour regulation and underlined the importance of individual, social and structural influences. Parenting skills (routine setting and the ability to manage the behaviour of a reluctant child) were emphasised as critical to the success of PSB. The multi-disciplinary intervention development group highlighted the need for both universal and targeted programmes, which could be implemented within current provision. Two intervention pathways were developed: a lower cost universal pathway utilising an existing national programme and an intensive targeted programme delivered via existing parenting programmes. A training manual was created to accompany each intervention to ensure knowledge and standardise implementation procedures. CONCLUSIONS: PSB is a complex behaviour and requires intervention across individual, social and structural levels. IM, although a time-consuming process, allowed us to capture this complexity and allowed us to develop two community-based intervention pathways covering both universal and targeted approaches, which can be integrated into current provision. Further research is needed to evaluate the acceptability and sustainability of these interventions
Barriers and attitudes influencing non-engagement in a peer feedback model to inform evidence for GP appraisal
<p>Abstract</p> <p>Background</p> <p>The UK general practitioner (GP) appraisal system is deemed to be an inadequate source of performance evidence to inform a future medical revalidation process. A long-running voluntary model of external peer review in the west of Scotland provides feedback by trained peers on the standard of GP colleagues' core appraisal activities and may 'add value' in strengthening the robustness of the current system in support of revalidation. A significant minority of GPs has participated in the peer feedback model, but a clear majority has yet to engage with it. We aimed to explore the views of non-participants to identify barriers to engagement and attitudes to external peer review as a means to inform the current appraisal system.</p> <p>Methods</p> <p>We conducted semi-structured interviews with a sample of west of Scotland GPs who had yet to participate in the peer review model. A thematic analysis of the interview transcriptions was conducted using a constant comparative approach.</p> <p>Results</p> <p>13 GPs were interviewed of whom nine were males. Four core themes were identified in relation to the perceived and experienced 'value' placed on the topics discussed and their relevance to routine clinical practice and professional appraisal: 1. Value of the appraisal improvement activity. 2. Value of external peer review. 3. Value of the external peer review model and host organisation and 4. Attitudes to external peer review.</p> <p>Conclusions</p> <p>GPs in this study questioned the 'value' of participation in the external peer review model and the national appraisal system over the standard of internal feedback received from immediate work colleagues. There was a limited understanding of the concept, context and purpose of external peer review and some distrust of the host educational provider. Future engagement with the model by these GPs is likely to be influenced by policy to improve the standard of appraisal and contractual related activities, rather than a self-directed recognition of learning needs.</p
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